Safety of ultra‐low contrast coronary angiography in patients with acute kidney injury

Abstract Background Ultra‐low contrast administration during coronary angiography has been previously shown to be feasible and safe among patients with stable chronic kidney disease. In the present study, we investigate the safety of ultra‐low contrast coronary angiography in patients with pre‐existing acute kidney injury (AKI). Methods The study was a retrospective single‐center evaluation of hospitalized patients who had AKI and required coronary angiography. Ultra‐low contrast use was defined as ≤18 mL of contrast media. Results The cohort consisted of a case series of eight inpatients with AKI who required coronary angiography. The mean age was 57 (±16) years and half were females. All patients had chronic kidney disease with a mean baseline estimated glomerular filtration rate of 34 (±17) mL/min/1.73 m2. The mean creatinine before angiography was 3 (±1) mg/dL and volume of contrast administered was 14 (±4) mL. One patient had a 0.1 mg/dL increase in creatinine during admission, and no patients had further AKI up to 1‐week postprocedure. Conclusions The current data suggest that ultra‐low contrast coronary angiography can be safely performed in patients with pre‐existing AKI The study should be viewed as hypothesis‐generating due to its small sample size. A larger cohort is required to validate the results.


| INTRODUCTION
Contrast-induced nephropathy (CIN) remains a major source of morbidity in contemporary invasive cardiology practice.There are several wellestablished risk factors, 1 including higher amounts of contrast agent administration during coronary angiography, 2 and chronic kidney disease (CKD). 3When CIN occurs, it is associated with adverse outcomes. 4,5erefore, various measures for prevention of CIN have been explored. 1dration protocols were shown to reduce the risk of CIN. 6,7Reducing volumes of contrast administration is also effective in preventing CIN. 8 Accordingly, methods for ultra-low use of contrast agents during coronary angiography were developed 9 and shown to be feasible and safe. 10revious studies evaluating ultra-low contrast coronary angiography and interventions included patients with CKD. 8,10,11The techniques have not been evaluated on patients with acute kidney injury (AKI).In the present study, we investigate the safety of ultra-low contrast coronary angiography in patients with pre-existing AKI.

| Population and definitions
The study was a case series from a single-center of patients with AKI who required coronary angiography over a 12-month period during 2022-2023.AKI was defined as an increase in serum creatinine (SCr) by ≥50% within 7 days or an increase in SCr by ≥0.3 mg/dl within 2 days. 12Baseline sCr levels were measured either on admission (n = 6) or on available laboratory tests during the week before the angiography (n = 2).The baseline sCr level was compared to the sCr level on the day of the angiography.All patients had stable sCr within the 24 h before angiography.Patients with AKI in whom the application of ultra-low contrast techniques was not practical, such as shock, ST-elevation myocardial infarction, respiratory failure, or hemodynamic instability, were not included in the analysis.Four hundred and twenty coronary angiographies were screened and 24 patients who clearly had AKI and had undergone coronary angiography without ultra-low contrast coronary angiography techniques were excluded.Ultra-low contrast coronary angiography was defined as administration of 18 ml of contrast or less during the index procedure.Methods for ultra-low contrast coronary angiography were previously described. 7,9In short, coronary artery engagement was performed using conventional coronary catheters and saline injections or guidewire-facilitated engagement.Large caliber catheters were avoided, and contrast was aspirated before catheter exchange.Contrast was diluted by approximately 30% with saline and cine frame rate was increased.Limited projections were performed and if further characterization of lesions was required intravascular ultrasound and/or instantaneous wave-free ratio were used.Management of renal dysfunction was left to the discretion of the primary team and guided by the etiology of AKI.There was no post-hydration protocol due to the low amount of contrast administration.Levels of sCR were documented at 24, 48, and 72 h after the angiography.CIN was defined as an increase in 0.5 mg/dL, or a relative rise of 25% from the baseline value. 13Estimated glomerular filtration rate was calculated using the CKD epidemiology collaboration formula. 14Risk for CIN was calculated using the Mehran score. 15The study was approved by the institutional review board (approval number 2023-421).

| Statistical analysis
Categorical variables were reported as numbers and percentages, and continuous variables were reported as means and standard deviations or median and interquartile range.Continuous variables were tested for normal distribution using histograms and Q-Q plots.

| RESULTS
The cohort consisted of eight inpatients with AKI who required coronary angiography.The mean age was 57 (±16) years and half were females.All patients had CKD with a mean baseline estimated glomerular filtration rate of 34 (±17) mL/min/1.73m 2 .Additional baseline characteristics are presented in Table 1.Mean sCr at admission was 3.3 (±1) mg/dL, and before angiography, 3 (±1) mg/dL.Procedural characteristics are presented in Table 2. Indications for coronary angiography included work-up for heart failure with reduced ejection fraction (n = 1), acute coronary syndrome (n = 3), pretranscatheter aortic valve replacement work-up (n = 1), and pre-renal transplant work-up (n = 3).A clinical correlation was observed in those with heart failure, while in the reminder of patients AKI was found in routine up lab results.Mean contrast volume used was 14 (±4) mL with contrast volume to estimated glomerular filtration rate ratio of 0.7 (±0.4).
One patient had a 0.1 mg/dL increase in creatinine during admission, and no other patient had worsening AKI. Figure 1 shows the mean change in creatinine before angiography to 48 h and 1 week after the procedure.Of note, among the 24 patients with AKI who did not receive ultra-low contrast coronary angiography during the study period there was 16.7% further AKI, and 25% had further increase in creatinine during the admission.Cardiorenal synrdome is also a cause for AKI. 12 Finally, additional coincidental etiologies of AKI that occur concomitentenly to coronary angiography could be the cause of peri-procdural AKI, and still fall under the definition of CIN.A relatively small amount of contrast agent exposure alone is much less likely to inflict AKI.Renal blood flow accounts for approximately 20% of the cardiac output.During coronary angiography, contrast material is diluted by the time it reaches the kidneys.In a scenario when contrast is administered in small amounts such as 10 mL, only 1 mL would reach each kidney per minute.Even if the contrast material is not filtered out and 5 mL remains in each kidney, it is unlikely to impact the global renal function, as reflected by serum creatinine.Accordingly, none of the patients in the current study showed worsening renal function.
Moreover, even low-contrast percutaneous coronary intervention was previously shown to be feasible and safe. 11,16evious studies showed the feasibility of coronary angiography in patients with CKD 10,11,17 and mean eGFR as low as 16 mL/min/ 1.73 m 2 . 10,11,17Median contrast administered was 8.8-13.5 mL 10,11 even among patients with prior coronary artery bypass grafts. 17netheless, in these studies, patients had reduced but stable renal function.Within the limitation of the cohort's sample size, the current data suggest that even urgent, non-emergent indications for coronary angiography can be safely performed on patients with AKI and a stabilized serum creatinine level.
Notably, although hospital stay is influenced mostly by the main problem since there was no further AKI in any of the patients, prevention of further deterioration of renal function by using ultralow contrast techniques potentially prevented delay in discharge.
Nevertheless, ultra-low contrast coronary angiography techniques are practical in a relatively stable population since they may be more time-consuming and, therefore, may not apply to those who require urgent procedures.
There are limitations to the study that must be regarded.This is a retrospective study that could be impacted by selection bias.
Additionally, the cohort was of small size.Conclusions relevant for a widespread population cannot be safely drawn and a larger prospective study is required to confirm the current results.
To conclude, the current data suggest that coronary angiography can be safely performed on patients with pre-existing AKI F I G U R E 1 Change in creatinine before angiography to 48 h and 1 week after the procedure.Dotted lines depict each patient; The solid line depicts the mean.